Method and means for desalting the operating fluid of a steam generator



United States Patent METHOD AND MEANS FOR DESALTING THE OPERATING FLUID OF A STEAM GENERATOR Application January 19, 1955, Serial No. 482,799 8 Claims. (or. 122-379 The invention relates to a method for desalting the operating fluid of a forced flow steam generator. The invention relates also to apparatus for performing the method.

An object of the present invention is to provide a method for desalting the operating fluid of a forced flow steam generator, which method ensures that only thoroughly purified steam enters the superheater. In the method according to the invention water is separated from the partly evaporated operating fiuid upstream of a heating surface zone' of the steam generator in which the water is completely evaporated and salt contained in the feed water is deposited on the heating surface. The separated water is by-passed around the final evaporating heating surface zone and the by-passed water is mixed with the steam produced in the aforesaid zone, which steam is slightly superheated, whereupon the water is separated from the so produced wet steam. For temporary washing-out of the final evaporating heating surface zone, the first water separating step may-be temporarily omitted and no water by-passed around the final evaporating zone, so that fluid containing no steam or only a small percentage of steam flows through the zone of the steam generator where salt is depoisted during normal operation. During the temporary washing-out periods the steam leaving the final evaporating heating surface zone is very wet and its moisture which contains salt is separated downstream of the final evaporating zone and blown down.

It is a further object of the invention to provide in a forced flow steam generating apparatus means suitable for performing the method described supra. The apparatus includes a primary water separator interposed inthe flow of the operating fluid between a primary evaporating heating surface and a final evaporating heating surface, a conduit connected with the primary water separator for by-passing separated water around the final evaporating heating surface zone and conducting the water'into the steam coming from the final evaporating heating surface zone, and a secondary water separator receiving the so produced steam-water mixture. A mixing container may be provided between the final evaporating heating surface zone and the secondary water separator, in which container the steam is mixed with the by-passed water. A valve is interposed in the by-pass conduit. The by-pass conduit may terminate in the secondary separator so that. the latter serves as mixing H container. A separate blow-down conduit is preferably connected with each separator and an adjustable flow control means may be provided in each blow-down conduit. The water separating system according to the invention can be used also in forced flow steam generators in which at least two evaporating heating surfaces are arranged in parallel with respect to the flow of the operating fluid and in which a single superheating surface section is provided for superheating the steam produced in the evaporating heating surface sections. In that case aprima'ry separator may be arranged upstream of each of 2,879,750 Patented Mar. 31, 1959 the final evaporating heating surface sections, and a secondary separator may be provided downstream of each of the final evaporating heating surface sections. The parallel heating surface sections upstream of the primary separators may be interconnected, so that the fluid coming from these heating surface sections is combined before it is distributed into the primary separators.

In the conventional systems for desalting the operating fluid of a forced flow steam generator a separator is arranged downstream of the salt separating or scaling zone of the evaporating surface for removing a portion of the salts contained in the feed water. In this case, a part of the evaporating surface is located in the zone where contaminated water is evaporated and salt is de posited, so that the heating surfaces may become sealed.

The present invention provides a method andmeans for elfectively avoiding salt incrustations, by diverting, upstream of. the scaling zone, a portion of the liquid from the partly evaporated fluid, by-passing the diverted liquid around the scaling zone, mixing the diverted liquid with the slightly superheated steam emerging from'the scaling zone, and thereupon separating the unevaporated liquid from the mixture. At certain intervals, particularly when salt deposits in the scaling zone necessitate desludging or washing out of the tube system forming the evaporating heating surface, removal of liquid and bypassing the liquid around the scaling section of the evaporating heating surface may be interrupted and the portion of the operating fluid which is not evaporated in the fin'al evaporator may be separated and .removed downstream of the final evaporating heating surface section.

The novel features which are considered characteristic of the invention are set forth with particularity in the appended claims. The invention itself however and additional objects and advantages thereof will best be understood from the following description of embodiments thereof when read in conjunction with the accompanying drawing, in which Fig. 1 is a diagram showing the arrangement of the heating surfaces, water separators, and desludging devices according to the invention in aforced flow steam generator;

Fig. 2 is a diagram showing the temperatures of the water and. steam flowing through the heating surfaces of a conventinal forced, flow steam generator;

Fig. 3 is a diagram like thediagram shown in Fig. 2 indicating, however, the water and steam temperatures in a steam generator equipped according to the present invention;

Fig. 4 illustrates a modified portion of the arrangement shown in Fig. l;

Fig. 5 illustrates another modification of a portion of the arrangement shown in Fig. 1;

Fig. 6 diagrammatically illustrates the system according to the invention 'as applied to a forced flow steam generator having at least two evaporating heating surface sections arranged in parallel with respect to the flow of the operating fluid.

The same numerals designate the same parts in all figures.

Referring more particularly to Fig. l of the drawing, the steam generator comprises heating surface sections 1, 2, 3, 4, and 5 which are interconnected in the conventional manner by conduits 7, 20, 21, 22, and 23, which may be in the form of downcomer tubes. The heating surface 1 constitutes a feed water preheater. The preheated water is evaporated in the heating surfaces 2, 3, and 4, the so generated steam being superheated in the heating section 5. Salts are separated in the last evaporating section 4. In the evaporating sections 2 and 3 there is enough water to prevent salt deposits. The feed water is forced into the steam generator through a tube 6 by means of a pump 8. The superheated steam is conducted through a steam main 9 to apparatus in which the steam is used. A water separator 11 is interposed in the conduit 21 which connects. the evaporating sections 3 and 4. A conduit 13 is connected to the separator 11 and by-passes the evaporating section 4, delivering water from the separator 11 into a mixing container 12 which is interposed in the conduit 22 connecting the heating section 4 with a second separator 14. A valve 19 is interposed in the by-pass conduit 13 for controlling the amount of fluid by-passing the heating section 4. Blow-down conduits 15 and 17 of the water separators 11 and 14, re spectively, are provided with flow control means, for example, a controllable orifice 16', as shown in the conduit 15, or a valve 18, as shown in theconduit 17.

The blow-down conduit 15, although desirable in plants in which the feed water is much contaminated, is not absolutely essential for performing the method according tothe invention.

The mixing container 12 may be omitted and the bypass conduit 13 may be connected with the conduit 22, as shown in Fig. 4.

Fig. illustrates an arrangement in which the separator 14 is also used as mixing container and the. bypass conduit13 terminates in the separator 14.

Fig. 2 illustrates the temperature of the operating lluid flowing through a conventional forced flow steam generator. The temperature rises in the feed water preheater 1 and drops somewhat in the evaporators 2, 3, and 4 due to a pressure decrease in these evaporators. The zone in which salt is separated is primarily in the neighborhood of point which is located in the evaporating section 4. This zone of maximum salt separation moves within the separator 4 depending on the operating conditions of the steam generator, such as amount of fluid pumped through the generator, amount of heat supplied to the generator, and the like. The point of maximum salt separation may move to the right, as indicated by numeral 10 in Fig. 2. It is not possible to purify the steam at a predetermined point or within a predetermined limited zone of the evaporating surface. Therefore, a separator is preferably arranged downstream of the heating surface 4, so that water which is saturated with salt can be blown down in the neighborhood of the zone in which salt separation is greatest. In order to avoid the shortcomings of the conventional arrangement, the invention provides a water separator-11 in the conduit 21 upstream of the heating surface section 4. A

portion of the water contained in the wet steam passing 7 through the conduit 21 and salt contained in the water is separated in the separator 11. A part of the separated water may be blown down through the adjustable orifice device 16, the remainder of the separated water being conducted through the conduit 13 into the mixing container 12. The amount of water flown through the bypass conduit 13 is controlled by the valve 19.

When starting the steam generating plant, a somewhat purified steam-water mixture enters the heating section 4, because of the action of the separator 11, so that dangerous salt deposits. will not occur in the section 4. The steam leaving the section 4 through the conduit 22 which steam is already somewhat superheated, is mixed in the container 12 with the water separated in the separator 11 and conducted through the conduit 13. The steam-water mixture produced in the container 12 is conducted into the separator 14 in which the liquid phase of the fluid is separated. The water coming from the first separator 11 contains a relatively small amount of salt=and has a purifying efiect onthe steam with which it is mixed in the container 12, in the conduit 22, and/or in the separator-14. Whereas the separator 11 acts as a preliminary and rough separator, the second separator 14acts as a fine separator,- so thatno salt will b? (l posited on the superheating surface 5. Y

Fig. 3 illustrates the temperature of the fluid passing through .a forced flow vapor generator which is equipped according to the invention. The zone of greatest salt separation is in the neighborhood of point 10 and may move to point 10' depending on the operating conditions of the generator. Any moisture left in the steam leaving the heating surface 4 plus the relatively small amount of liquid and salt coming from the preliminary separator 11 through the conduit 13 is removed in the separator 14, pure steam leaving the latter.

Only such an amount of liquid is taken from the sop-- arator 11 and conducted through the conduit 13 and mixed with the steam leaving the evaporating sectionv 4, as is suflicient to make the steam sutliciently wet to effeet a satisfactory separation in the secondary separator 14. If desired, liquid containing salt may be blown down through the conduits 15 and 17 into the atmosphere, or may be conducted to places where the hot water can be used. The main blow-down operation is performed through the conduit 17 which is connected with the separator 14 and controlled by the valve 18. The flow control means 16, 18, and 19 may be operated in the conventional manner in dependence on operating conditions of the steam generator. If it is desired that the salt separating zone in the heating section 4 be temporarily washed out, the flow control means 16 and 19 are closed, so that predominantly liquid medium flows through the section 4. The relatively great amount of liquid which is not evaporated in the section 4 is sep arated in the separator 14.

Fig. 3 showsa drop of temperature at the point where water separated in the separator 11 is mixed with the somewhat superheated steam in conduit 22 because the superheated steam is converted into wet steam. The heating sections 1 to 4 must therefore be operated at somewhat higher temperatures than those in a conventional steam generator to obtain the same temperature at the outlet of the superheater 5.

In forced flow steam generators in which the individual heating sections are arranged pairwise and in parallel with respect to the flow of the operating medium, primary separators are preferably provided upstream of each section in which the operating medium is evap orated, and a secondary separator is provided downstream of each section in which the operating medium is evaporated. A single superheating section may receive the vapor producedin the parallel arranged evaporating sections. It may be of advantage to shortcircuit the parallelarranged heating sections upstream of. the. prev liminary separators prior to the distribution of: the fluid. into the primary separators. Such a system is illustrated in Fig. 6 in which two primary evaporating sections 2 and 3' are arranged in parallelwith respect to the flow of the operating fluid. The. medium emerging from the two sections 2' and 3 is united in a com duit 21 and thereupon distributed into two primary separators 11 and 11". A final evaporating unit is. connected with each of the separators for receiving. wet steam from the latter. At the outlet of each final evaporating unit 4? and 4" a separator 14' and 14?, respectively, is provided. The water separated in the primary separator 11 by-passes the unit 4' through a conduit 13' and is united with the steam leaving this unit before the steam enters the separator 14. The water separated in the separator 11" by-passes the unit 4' through a conduit 13" and is united with the steam leaving the unit 4" before the steam entersthe separator14". The purified steam emerging from the separators14' and 14"is united in a conduit 23' and conducted into a single superheater section 5'.

While specific embodiments of the invention have been shown and described, it will be apparent to those skilled in the art that various changes, modifications, substitutions, additions and omissions may be made therein without departing from the spirit and scope of the invention as set forth in the appended claims.

What is claimed is:

1. In a forced flow steam generator having a heated tube system through which the operating fluid is conducted for heating the flowing operating medium and changing the fluid from the water state into the steam state, said tube system including a primary evaporating section in which a relatively small portion of the water is vaporized, a final evaporating section in which operating fluid is fully evaporated, and a superheater section in which the so produced steam is superheated: a system for desalting the operating fluid including a primary water separator connected with said primary evaporating section for receiving operating fluid therefrom, said water separator having a steam space connected with said final evaporating section for discharging relatively wet steam thereinto, a secondary water separator connected with said final evaporating section for receiving operating fluid therefrom and having a steam space connected with said superheater for discharging substantially dry steam thereinto, said primary water separator having a liquid space, and a pipe interconnecting said liquid space and said tube system downstream of said final evaporating section for conducting relatively cool water separated in said primary separator into the relatively dry steam entering said secondary water separator for wetting the dry steam and promoting separation of water containing salt in said secondary water separator.

2. In a forced flow steam generator as defined in claim 1 and wherein said desalting system includes a mixing means interposed in said tube system between said final evaporating section and said secondary water separator and said pipe terminates in said mixing means.

3. In a forced flow steam generator as defined in claim 1 and wherein a valve is interposed in said pipe.

4. In a forced flow steam generator as defined in claim 1 and wherein said pipe terminates in said secondary water separator.

5. In a forced flow steam generator as defined in claim 1 and wherein each of said water separators is provided with a blow-down conduit and a flow control means is provided in each of said blow-down conduits.

6. In a forced flow steam generator as defined in claim 1 and wherein said final evaporating section includes at least two tubular conduits arranged in parallel with respect to the flow of the operating fluid, a primary water separator being connected with the inlet of each of said tubular conduits for discharging relatively wet steam thereinto, a secondary water separator being connected with the outlet of each of said tubular conduits for receiving operating medium therefrom, a pipe being connected with the water space of each of said primary water separators and terminating in the outlet of the respective tubular conduit, said superheater section being formed by a single tubular conduit, and the steam spaces of all of said secondary water separators being connected with said single tubular conduit.

7. A method for desalting the operating fluid of a forced flow steam generator and for periodically washing out the steam generator including the steps of separating water, in a first separating step, from the partly evaporated operating fluid leaving a primary evaporating section of the steam generator, of drying the steam separated from the water in a final evaporating section of the steam generator, of conducting water separated in said first separating step around said final evaporating section and into the steam emerging from the final evaporating section for wetting the steam emerging from the final evaporating section, of separating water containing salt, in a second separating step, from the so produced wet steam, of superheating, in a superheater, the steam separated in the second separating step, and of temporarily discontinuing said first separating step and conducting all water emerging from the primary evaporating section into and through the final evaporating section of the steam generator, for washing out the final evaporating section While temporarily evaporating, in the superheater, water emerging from the final evaporating section.

8. A method for desalting the operating fluid of a forced flow steam generator and for periodically washing out the steam generator including the steps of separating water, in a first separating step, from the partly evaporated operating fluid leaving a primary evaporating section of the steam generator and blowing off a portion of the separated water, of drying the steam separated from the water in a final evaporating section of the steam generator, of conducting the balance of the water separated in said first separating step around said final evaporating section and into the steam emerging from the final evaporating section for wetting the steam emerging from the final evaporating section, of separating water containing salt, in a second separating step, from the so produced wet steam, of superheatiug, in a superheater, the steam separated in the second separating step, and of temporarily stopping flow of operating medium around the final evaporating section and of temporarily stopping blowing ofl water upstream of the final evaporating section and conducting all water emerging from the primary evaporating section through the final evaporating section of the steam generator for washing out the final evaporating section while temporarily evaporating, in the superheater, water emerging from the final evaporating section.

References Cited in the file of this patent UNITED STATES PATENTS 2,032,924 Eule Mar. 3, 1936 2,614,543 Hood Oct. 21, 1952 FOREIGN PATENTS 515,097 Belgium Nov. 14, 1952 693,330 Great Britain June 24, 1953 282,191 Switzerland Aug. 1, 1952 95,805 Switzerland V May 30, 1939 

